The present invention relates to a process of producing lithium manganate. More particularly it relates to a process of lithium manganate production which hardly causes particles to be sintered during firing, reduces iron incorporation, and provides lithium manganate exhibiting satisfactory battery characteristics when used as a cathode material of a nonaqueous secondary battery.
With the recent rapid development of portable and wireless electronic equipment such as personal computers and telephones, the demand for secondary batteries as a driving power source has been increasing. In particular nonaqueous secondary batteries are expected for their smallest size and high energy density. Cathode materials for nonaqueous secondary batteries meeting the demand include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMn2O4), etc. Having an electrode potential of 4 V or higher with respect to lithium, these complex oxides are capable of providing batteries having a high energy density.
Of the above-described complex oxides, LiCoO2 and LiNiO2 have a theoretical capacity of about 280 mAh/g, while LiMn2O4 has a theoretical capacity as low as 148 mAh/g but is deemed suited for use in electric vehicles and the like because of an abundant and inexpensive supply of manganese oxide as a raw material and freedom from such thermal instability in charging as observed with LiNiO2.
Electrolytic manganese dioxide is a suitable manganese source of lithium manganate (LiMn2O4) for its inexpensiveness and abundance. Electrodeposited manganese dioxide is usually crushed and neutralized for use as a manganese raw material.
The crushed and neutralized electrolytic manganese dioxide has an average particle size of about 20 to 40 xcexcm. It should be pulverized to an average size of about 5 xcexcm which is suitable as a manganese raw material. However, the electrolytic manganese dioxide obtained by conventional pulverization has an average particle size of about 10 xcexcm. Where lithium manganate prepared from such electrolytic manganese dioxide is used as a cathode material for nonaqueous secondary batteries, there arise problems that the coating properties are poor, and high-rate characteristics are impaired. Moreover, there is another problem that impurities such as iron may be incorporated into the electrolytic manganese dioxide, which adversely affects the properties of lithium manganate.
The pulverization is accompanied by generation of fine particles of the electrolytic manganese dioxide, which, if used as a manganese raw material, tends to accelerate sintering among particles while fired with a lithium raw material.
Accordingly, it is an object of the present invention to provide a process for producing lithium manganate, which hardly causes particles to be sintered during firing, reduces iron incorporation, and provides lithium manganate exhibiting satisfactory battery characteristics when used as a cathode material of a nonaqueous secondary battery.
As a result of studies, the present inventors have found that the above object is accomplished by pulverizing electrolytic manganese dioxide in a pulverizer of the system in which particles are made to collide with each other into particles of about 5 xcexcm as a raw material of lithium manganate and recovering fine particles by-produced in the pulverization.
The present invention has been completed based on the above finding and provides a process of producing lithium manganate which is characterized by comprising pulverizing electrodeposited manganese dioxide having been crushed and neutralized in a pulverizer of the system in which particles are made to collide with each other, screening the grinds, mixing the resulting electrolytic manganese dioxide having an average particle size of 3 to 20 xcexcm with a lithium raw material, and firing the mixture.